Systematic Orbital Geometry-Dependent Variations in Satellite Solar-Induced Fluorescence (SIF) Retrievals
Year: 2020
Type: article
Abstract: While solar-induced fluorescence (SIF) shows promise as a remotely-sensed measurement directly related to photosynthesis, interpretation and validation of satellite-based SIF retrievals remains a challenge. SIF is influenced by the fraction of absorbed photosynthetically-active radiation at the canopy level that depends upon illumination geometry as well as the escape of SIF through the canopy that depends upon the viewing geometry. Several approaches to estimate the effects of sun-sensor geometry on satellite-based SIF have been proposed, and some have been implemented, most relying upon satellite reflectance measurements and/or other ancillary data sets. These approaches, designed to ultimately estimate intrinsic or physiological components of SIF related to photosynthesis, have not generally been applied globally to satellite measurements. Here, we examine in detail how SIF and related reflectance-based indices from wide swath polar orbiting satellites in low Earth orbit vary systematically due to the host satellite orbital characteristics. We compare SIF and reflectance-based parameters from the Global Ozone Mapping Experiment 2 (GOME-2) on the MetOp-B platform and from the TROPOspheric Monitoring Instrument (TROPOMI) on the Sentinel 5 Precursor satellite with a focus on high northern latitudes in summer where observations at similar geometries and local times occur. We show that GOME-2 and TROPOMI SIF observations agree nearly to within estimated uncertainties when they are compared at similar observing geometries. We show that the cross-track dependence of SIF normalized by PAR and related reflectance-based indices are highly correlated for dense canopies, but diverge substantially as the vegetation within a field-of-view becomes more sparse. This has implications for approaches that utilize reflectance measurements to help account for SIF geometrical dependences in satellite measurements. To further help interpret the GOME-2 and TROPOMI SIF observations, we simulated cross-track dependences of PAR normalized SIF and reflectance-based indices with the one dimensional Soil-Canopy Observation Photosynthesis and Energy fluxes (SCOPE) canopy radiative transfer model at sun–satellite geometries that occur across the wide swaths of these instruments and examine the geometrical dependencies of the various components (e.g., fraction of absorbed PAR, SIF yield, and escape of SIF from the canopy) of the observed SIF signal. The simulations show that most of the cross-track variations in SIF result from the escape of SIF through the scattering canopy and not the illumination.
Source: Remote Sensing
DOI: 10.3390/rs12152346
Institutions: Goddard Space Flight Center, National Aeronautics and Space Administration, Science Systems and Applications (United States), California Institute of Technology, University of Maryland, Baltimore County, Jet Propulsion Laboratory, International Institute for Geo-Information Science and Earth Observation, University of Twente, Universitat Politècnica de València, Cornell University, New York State College of Agriculture & Life Sciences
Language: English
Subfield: Ecology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,324
Awards: G3949843927, G686194536, LAND COVER USE PRACTICES AND THE ONGOING HUMAN ACTIVITIES AND CLIMATE CHANGES HAVE SIGNIFICANTLY AFFECTED AGRICULTURAL AND FOREST PRODUCTIVITY BY IMPOSING SEVERE AND NOVEL COMBINATIONS OF MULTIPLE STRESSES ON THE NATURAL ECOSYSTEMS. THERE IS A STRONG NEED TO DEVELOP AN APPROACH FOR QUANTIFYING THE SPATEO-TEMPORAL CHANGES IN VEGETATION CONDITION AND PHOTOSYNTHETIC FUNCTION AT MODERATE GROUND RESOLUTION (20-30 M) ACROSS LARGE REGIONAL/CONTINENTAL/GLOBAL SCALES. IN THE SPRING OF 2015 ESA S SENTINEL-2 (S-2) SATELLITE JOINED NASA S LANDSAT-8 (L-8) IN PROVIDING MODERATE-RESOLUTION MULTISPECTRAL MEASUREMENTS WITH GLOBAL EXTENT THEREFORE INCREASING THE TEMPORAL RESOLUTION OF SUCH DATA. WE PROPOSE TO USE THE RECENTLY DEVELOPED HOMOGENIZED L-8 AND S-2 (HLS) HIGH-FREQUENCY TIME SERIES TO DEVELOP A NEW CANOPY CHLOROPHYLL CONTENT PRODUCT AND TO EVALUATE THE SEASONAL CHANGES IN LAND COVER CHLOROPHYLL CONTENT AND ASSOCIATED PRODUCTIVITY FOR KEY AGRICULTURAL CROPS GRASSLANDS AND FORESTED ECOSYSTEMS. THE KEY OBJECTIVES OF THE PROPOSED EFFORT ARE TO: 1) USING IN A SEAMLESS FASHION THE DENSE TIME SERIES OF HLS L-8 AND S-2 IMAGES TO DEVELOP ALGORITHMS FOR ESTIMATING CANOPY CHLOROPHYLL (CHL) CONTENT; AND 2) GENERATE ROBUST WORKFLOWS AND PRODUCE HIGH DENSITY TIME SERIES OF LAND COVER CHL PRODUCTS FOR MAJOR VEGETATION COVER TYPES (CROPS GRASSLANDS AND FORESTS). EARLIER STUDIES USING INDIVIDUAL LANDSAT SCENES (E.G. LANDSATS TM AND ETM+) WERE NOT ABLE TO DETECT THE EARLY STAGES IN VEGETATION DAMAGE. THOSE STUDIES ONLY PARTIALLY ACCOUNTED FOR VARIATIONS IN ATMOSPHERIC CONDITIONS TERRAIN ELEVATION AND ILLUMINATION. USING THE IMPROVED SPECTRAL RESOLUTION OF THE HLS L-8 AND S-2 DATA (NARROWER RED EDGE BANDS AND ADDITIONAL BLUE NEAR-INFRARED SHORT-INFRARED AND THERMAL BANDS) COMPLEMENTED WITH VERY HIGH RESOLUTION (2 M) WORLD VIEW IMAGES/TRIPLETS TO CHARACTERIZE CANOPY VARIATIONS AND STRUCTURAL EFFECTS WE WILL PRODUCE DENSE TIME SERIES OF VEGETATION INDICES AND CHL PRODUCTS SENSITIVE TO THE FINE CHANGES IN CHLOROPHYLL CONTENT FOR IMPROVED MONITORING OF AGRICULTURAL CROPS AND FOREST BIOMASS PRODUCTION. TO GENERATE ROBUST WORKFLOWS THE ALGORITHMS WILL BE TESTED REFINED AND VALIDATED AT ESTABLISHED RESEARCH AREAS AND INSTRUMENTED SITES REPRESENTING MAJOR AGRICULTURAL CROPS AND FORESTED ECOSYSTEMS. WE WILL USE THE L-8 THERMAL BANDS (TIRS1) TO QUANTIFY THE EFFECTS FROM CHANGES IN CHL CONTENT AND VEGETATION DAMAGE ON AGRICULTURAL AND FOREST PRODUCTIVITY COMPARING THE PHENOLOGY TRENDS IN CANOPY CHL TIRS1 AND ECOSYSTEM PRIMARY PRODUCTION AS MEASURED AT THE SITES. BY ANALYZING THESE COUPLED DENSE TIME SERIES WE WILL PROVIDE ESSENTIAL INFORMATION ABOUT THE MAJOR BIOPHYSICAL DRIVERS OF VEGETATION HEALTH AND FUNCTION. THIS EFFORT LEVERAGES THE ONGOING INTERNATIONAL COLLABORATIONS BETWEEN USA AND EUROPEAN UNION RESEARCHERS WHICH WILL PROVIDE EXPERTISE AND SATELLITE IMAGERY AVAILABLE AT THEIR ORGANIZATIONS AS WELL AS FIELD SPECTRAL DATA OBTAINED FROM ESTABLISHED SITES WITH ONGOING FIELD DATA COLLECTIONS. THE PROPOSED WORK DIRECTLY SUPPORTS THE GOALS OF NASA S LCLUC PROGRAM TO FURTHER "DEVELOP THE CAPABILITY FOR PERIODIC SATELLITE-BASED INVENTORIES OF LAND COVER AND MONITORING AND CHARACTERIZING LAND-COVER AND LAND-USE CHANGE." THIS EFFORT PROVIDES A SIGNIFICANT STEP FORWARD TOWARDS DEVELOPING AN APPROACH AND TOOLS FOR EVALUATION OF VEGETATION HEALTH AND PHOTOSYNTHETIC FUNCTION AT 30 M RESOLUTION THAT WILL ENHANCE OUR ABILITY TO IDENTIFY THE DRIVERS AND QUANTIFY THE RATES OF LAND COVER CHANGE FOR CRITICAL VEGETATION TYPES ACROSS THE GLOBE. THIS ENHANCED CAPABILITY WILL GREATLY IMPROVE THE INFORMATION AVAILABLE FOR TIMELY MANAGEMENT DECISIONS THAT HAVE POTENTIAL TO REDUCE THE ASSOCIATED AGRICULTURAL ECONOMIC AND CLIMATE IMPACTS OF ENVIRONMENTAL AND ANTHROPOGENIC FACTORS.
OpenAlex ID: W3045443823